The present disclosure relates to subject matter contained in Japanese Patent Application No. 9-212776 (filed on Aug. 7, 1997) and Japanese Patent Application No. 9-268293 (filed on Oct. 1, 1997), which are expressly incorporated herein by reference in their entireties.
1. Field of the Invention
The present invention relates to a wire loop type instrument for an endoscope, such as a high-frequency snare. The present invention also relates to a method of producing such a wire loop type instrument.
2. Description of the Prior Art
A wire loop type instrument for an endoscope, e.g. a high-frequency snare, is generally arranged as shown in FIG. 1. An elastic wire 10 is formed from a stranded wire. The elastic wire 10 is bent into a U-shape at the distal end thereof and expanded in a loop shape at the rear of the U-shaped bent portion. When withdrawn into the distal end of a sheath 20, the elastic wire 10 is folded. When projecting from the distal end of the sheath 20, the elastic wire 10 expands in the loop shape by its own elasticity.
An example of the elastic wire 10 which has heretofore been widely used in such a wire loop type instrument includes a 1.times.7 stranded wire formed by twisting together seven strands 11 of stainless steel. Each strand 11 has a circular cross-sectional configuration with a diameter of the order of from 0.1 mm to 0.15 mm, as shown in FIG. 10.
In addition to the 1.times.7 stranded wire, various stranded wires are commonly used. Examples include a 1.times.3 stranded wire formed by twisting together three strands, a 1.times.19 stranded wire having 19 strands twisted together, and a 1.times.37 stranded wire containing 37 twisted strands.
FIG. 11 shows elastic wire 10 formed from a 1.times.7 stranded wire. When this wire is bent into a U-shape as shown by the chain double-dashed line, each strand 11 is loosened and irregularly deformed as shown in FIG. 12. Consequently, the arrangement of the strands 11 is disordered
As a result, the bent portion of the elastic wire 10 swells, and the wire 10 may become impossible to withdraw into the sheath 20. In actual use, the bent portion may be readily broken by the stress concentration or Joule's heat generated by the high-frequency electric current when a polyp or the like is pinched tight with the elastic wire 10. Moreover, the deformed elastic wire 10 locks inferior, causing the commercial value of the wire loop type instrument to be lowered.